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MathGroup Archive 2004

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Re: Forcing Argument Evaluation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49906] Re: [mg49848] Forcing Argument Evaluation
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Thu, 5 Aug 2004 09:22:28 -0400 (EDT)
  • References: <200408041446.KAA20125@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 4 Aug 2004, at 16:46, Scott Guthery wrote:
>
> f[x_] := x^2;
> a = {f,f/2};
>
> a[[1]][2]
> 4
>
> a[[2]][[2]
> f/2[2]
>
> I know I'm missing something fundamental.
>
> Cheers, Scott
>
>

It's the same problem again, which I already once explained. The 
algebra of functions is not implemented in Mathematica so although f is 
a function f/2 is not a function. So you can't expect f/2[2] to have 
return anything. If you really want implement the algebra of fucntions 
you could do something like this:




Unprotect[Times,Plus];

(a_?NumericQ * f_)[x_]:=a f[x]
(f_+g_)[x_]:=f[x]+g[x]
(f_*g_)[x_]:=f[x]*g[x]

Protect[Times,Plus]

Now

f[x_]:=x^2;
a={f,f/2};


a[[2]][2]
2



Andrzej Kozlowski
Chiba, Japan
http://www.mimuw.edu.pl/~akoz/


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